Semiconductor memory device and method of manufacturing the same

ABSTRACT

A semiconductor memory device includes a semiconductor substrate having a first region and a second region, a transistor placed in the first region of the semiconductor substrate, a first insulating film formed on the semiconductor substrate in the first and second regions and on the transistor, a first ferroelectric capacitor formed on the first insulating film in the first region and electrically connected to the transistor, a hydrogen barrier film formed above the first ferroelectric capacitor and above the first insulating film in the first and second regions, a first contact penetrating the hydrogen barrier film in the first region and electrically connected to the first ferroelectric capacitor, and a second contact which penetrates the hydrogen barrier film in the second region and which is in a floating state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2003-398162, filed Nov. 27, 2003,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory devicecomprising a ferroelectric capacitor and a method of manufacturing thissemiconductor memory device.

2. Description of the Related Art

Nonvolatile memories (hereinafter referred to as FeRAMs: FerroelectricRandom Access Memories) having a capacitor portion composed of aferroelectric substance can be used for high speed operations withoutany batteries. Accordingly, the FeRAM is now often mounted in anon-contact card such as an RF-ID by being mixed with a logic circuit orthe like. The FeRAM is also expected to be a memory that replacesconventional SRAMs (Static Random Access Memories), flash memories, andDRAMs (Dynamic Random Access Memories).

The conventional FeRAM is formed using, for example, the processdescribed below. First, a transistor is formed on a silicon substrate.Then, a first interlayer insulating film is deposited on the transistor.The first interlayer insulating film is then flattened. Then, aferroelectric capacitor is formed on the first interlayer insulatingfilm. Subsequently, annealing is carried out to recover theferroelectric capacitor from possible damage. Then, a hydrogen barrierfilm is deposited on the ferroelectric capacitor. Then, a secondinterlayer insulating film is deposited on the hydrogen barrier film.The second interlayer insulating film is then flattened. Then, contactholes are formed through the second interlayer insulating film and thehydrogen barrier film. Subsequently, annealing is carried out to recoverthe ferroelectric capacitor from possible damage. Then, a metal materialis filled into the contact holes to form contacts. Subsequently,interlayer insulating films or multilayer interconnects are formed asrequired.

Such a conventional FeRAM has the problems described below. Theferroelectric characteristic of the ferroelectric capacitor is known tobe degraded in a hydrogen atmosphere. Thus, to prevent the capacitorfrom being degraded in the hydrogen atmosphere during an interconnectionstep after the capacitor has been formed, a hydrogen barrier film isnormally formed on the capacitor. However, the hydrogen barrier filminhibits hydrogen from diffusing from a surface of a wafer to theinterior of the capacitor. Consequently, the hydrogen barrier film mayinhibit the diffusion of water molecules, which have a larger molecularweight than hydrogen. That is, the hydrogen barrier film may produce asecondary effect of suppressing the release of gases from under thehydrogen barrier film. As a result, when annealing is carried out torecover the capacitor from possible damage done to the capacitor duringprocessing, volatile components such as moistures and gases may begenerated from the interlayer insulating film. The volatile componentsare deposited immediately below the hydrogen barrier film at a highconcentration owing to the secondary effect.

Under these circumstances, when contact holes are formed through thehydrogen barrier film, the volatile components accumulated through thecontact holes are explosively diffused. The explosive release of gasesmay cause voids to be formed in the contact holes when a metal materialis filled into the contact holes to form contacts. Disadvantageously,this may prevent the contacts from being appropriately filled, thus, forexample, degrading the reliability of interconnects.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda semiconductor memory device comprising a semiconductor substratehaving a first region and a second region, a transistor placed in thefirst region of the semiconductor substrate, a first insulating filmformed on the semiconductor substrate in the first and second regionsand on the transistor, a first ferroelectric capacitor formed on thefirst insulating film in the first region and electrically connected tothe transistor, a hydrogen barrier film formed above the firstferroelectric capacitor and above the first insulating film in the firstand second regions, a first contact penetrating the hydrogen barrierfilm in the first region and electrically connected to the firstferroelectric capacitor, and a second contact which penetrates thehydrogen barrier film in the second region and which is in a floatingstate.

According to a second aspect of the present invention, there is provideda method of manufacturing a semiconductor memory device, the methodcomprising forming a transistor in a first region of a semiconductorsubstrate having the first region and a second region, forming a firstinsulating film in the first and second regions of the semiconductorsubstrate and on the transistor, forming a first ferroelectric capacitoron the first insulating film in the first region, the firstferroelectric capacitor being electrically connected to the transistor,forming a hydrogen barrier film above the first ferroelectric capacitorand above the first insulating film in the first and second regions,forming a second insulating film on the hydrogen barrier film, forming afirst contact hole penetrating the hydrogen barrier film in the firstregion to expose a top surface of the first ferroelectric capacitor andforming a second contact hole penetrating the hydrogen barrier film inthe second region, carrying out annealing, filling a metal material intothe first and second contact holes to form a first contact connected tothe first ferroelectric capacitor and a second contact which is in afloating state.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view showing a semiconductor memory device according toa first embodiment of the present invention;

FIG. 2 is a sectional view of a semiconductor device taken along a lineII-II in FIG. 1;

FIG. 3 is a sectional view showing a step of manufacturing asemiconductor memory device according to the first embodiment of thepresent invention;

FIG. 4 is a sectional view showing a continued part of FIG. 3 andshowing a step of manufacturing a semiconductor memory device accordingto the first embodiment of the present invention;

FIG. 5 is a sectional view showing a continued part of FIG. 4 andshowing a step of manufacturing a semiconductor memory device accordingto the first embodiment of the present invention;

FIG. 6 is a sectional view showing a continued part of FIG. 5 andshowing a step of manufacturing a semiconductor memory device accordingto the first embodiment of the present invention;

FIG. 7 is a sectional view showing a variation of the semiconductormemory device according to the first embodiment of the presentinvention;

FIG. 8 is a sectional view showing a variation of the semiconductormemory device according to the first embodiment of the presentinvention;

FIG. 9 is a plan view showing a semiconductor memory device according toa second embodiment of the present invention;

FIG. 10 is a sectional view of a semiconductor device taken along a lineX-X in FIG. 9;

FIG. 11 is a sectional view showing a step of manufacturing asemiconductor memory device according to the second embodiment of thepresent invention;

FIG. 12 is a sectional view showing a continued part of FIG. 11 andshowing a step of manufacturing a semiconductor memory device accordingto the second embodiment of the present invention;

FIG. 13 is a sectional view showing a variation of the semiconductormemory device according to the second embodiment of the presentinvention;

FIG. 14 is a sectional view showing a variation of the semiconductormemory device according to the second embodiment of the presentinvention; and

FIG. 15 is a sectional view showing a variation of the semiconductormemory device according to the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. In the description below, parts common to allthe drawings are denoted by the same reference numerals.

First Embodiment

A first embodiment is an example in which the evaporation of gassesaccumulated under a hydrogen barrier film is controlled by forming adummy capacitor and a dummy capacitor contact in a peripheral circuitportion in which capacitors or the like are conventionally not present.

FIGS. 1 and 2 show a semiconductor memory device according to a firstembodiment of the present invention. As shown in FIGS. 1 and 2, in aperipheral circuit portion, a dummy ferroelectric capacitor 25 b havingan upper electrode 23, a ferroelectric film 22, and a lower electrode 21is formed on a first interlayer insulating film 18. A hydrogen barrierfilm 26 is formed on the capacitor 25 b. A dummy capacitor contact 30 bis provided so as to penetrate the hydrogen barrier film 26 to connectto the capacitor 25 b. At least one end of a dummy element composed ofthe capacitor 25 b and the contact 30 b is not electrically connected toother interconnects or elements and is in a floating state.Consequently, no current flows through the capacitor 25 b or the contact30 b. Further, the capacitor 25 b and contact 30 b in the peripheralcircuit portion are arranged at the same levels as those at which acapacitor 25 a and a contact 30 a in a memory cell portion are arranged.The capacitor 25 b and the contact 30 b are also formed simultaneouslywith the capacitor 25 a and contact 30 a so as to have the same shapesas those of them, using the same materials as those of them.Interconnects 31 c, 31 d, 31 e, and 31 f arranged on a second interlayerinsulating film 27 and the contact 30 b need not be connected togetherprovided that they are in the floating state.

In the memory cell portion, a transistor 16 is formed by forming a gateelectrode 14 on a silicon substrate 11 via a gate insulating film 12 andforming a source/drain diffusion layer 15 in the silicon substrate 11 atopposite sides of the gate electrode 14. The first interlayer insulatingfilm 18 is formed so as to cover the transistor 16. A contact 19 isformed in the first interlayer insulating film 18 so as to connect tothe source/drain diffusion layer 15. The ferroelectric capacitor 25 ahaving the upper electrode 23, ferroelectric film 22, and lowerelectrode 21 is formed on the contact 19. The hydrogen barrier film 26is formed so as to cover the capacitor 25 a and the first interlayerinsulating film 18. The second interlayer insulating film 27 is formedon the hydrogen barrier film. Interconnects 31 a and 31 b are formed onthe second interlayer insulating film 27. The interconnect 31 a isconnected to the source/drain diffusion layer 15 via a contact 30 dpenetrating the interlayer insulating films 18 and 27 and the hydrogenbarrier film 26. The interconnect 31 b is connected to the upperelectrode 23 of the capacitor 25 a via the contact 30 a, penetrating theinterlayer insulating film 27 and the hydrogen barrier film 26.

In the memory cell portion and the peripheral circuit portion, an oxygenbarrier film 20 is provided under each of the capacitors 25 a and 25 b.A hard mask layer 24 is provided on each of the capacitors 25 a and 25b. The oxygen barrier film 20 in the memory cell portion can prevent thecontact 19 from being oxidized during annealing, which is required tocrystallize a ferroelectric substance or during annealing required torecover the processed ferroelectric film 22 from possible damage. Thehard mask layer 24 is used as a mask in processing the capacitors 25 aand 25 b. For example, the hard mask layer 24 composed of a PECVD(Plasma Enhanced Chemical Vapor Deposition)—SiO₂ film is left after thecapacitors 25 a and 25 b have been formed.

FIGS. 3 to 6 are sectional views showing steps of manufacturing asemiconductor memory device according to a first embodiment of thepresent invention. Description will be given of the method ofmanufacturing a semiconductor memory device according to the firstembodiment.

First, as shown in FIG. 3, the gate insulating film 12 composed of, forexample, an SiN film is formed on the silicon film 11. An elementisolation region 13 having an STI (Shallow Trench Isolation) structureis formed in the silicon substrate 11. Then, the gate electrode 14 isformed on the silicon substrate 11 in the memory cell portion via thegate insulating film 12. The source/drain diffusion layer 15 is thenformed in the silicon substrate 11 at the opposite sides of the gateelectrode 14. In this manner, the transistor 16, for example, a CMOS, isformed. Then, the insulating film 17 is formed on a top and bottomsurfaces of the gate electrode 14. Then, the first interlayer insulatingfilm 18 composed of, for example, a BPSG (Boron Phosphorous SilicateGlass) film is deposited on the transistor 16 and the silicon substrate11. The first interlayer insulating film 18 is then flattened using CMP(Chemical Mechanical Polish). Subsequently, the contact 19 is formed inthe first interlayer insulating film 18 in order to electrically connectthe capacitor and the transistor 16 together. A desirable materialfilled into the contact 19 is tungsten, which serves to reduceresistance, but may be polysilicon.

Then, as shown in FIG. 4, the oxygen barrier film 20, the lowerelectrode 21, the ferroelectric film 22, and the upper electrode 23 aresequentially deposited on the first interlayer insulating film 18 andthe contact 19.

An effective material for the lower electrode 21 is, for example,platinum, iridium, iridium oxide, strontium ruthenium oxide (SrRuO₃;hereinafter referred to as SRO), or their combination. The oxygenbarrier film 20 may be formed of a titanium-based material or atitanium/aluminum-based material. The structure of a stacked filmcomposed of the oxygen barrier film 20 and lower electrode 21 is, forexample, a combination of Pt/Ti/TiN, SRO/Pt/Ti/TiN, IrO₂/Ir/Ti/TiN, orIrO₂/Ir/TiAlN/TiN. If the stacked film composed of the oxygen barrierfilm 20 and the lower electrode 21 is IrO₂/Ir/TiAlN/TiN, the materialsmay be deposited so that the layers have a thickness of, for example,30, 30, 30, and 50 nm, respectively.

A useful material for the ferroelectric film 22 is PZT because it has alarge remanence polarization. However, strontium bismuth titanate oxide(bismuth-based laminar perovskite; hereinafter referred to as SBT) orthe like may be employed in place of PZT. The ferroelectric film 22 isdeposited to a thickness of about 150 nm using a sputtering process.However, instead of the sputtering process, a sol-gel process or a MOCVD(Metal Organic Chemical Vapor Deposition) process may be used to formthe film. The ferroelectric film 22 is crystallized by, for example,being annealed in a pure oxygen atmosphere at 600° C. for one hour.

If the upper electrode 23 is composed only of Pt, it is easily fatiguedwhen subjected to repeated writes and reads. Accordingly, a desirablematerial is, for example, a stacked film of Ir/IrO₂, a stacked film ofPt/SRO, or a stacked film of Ir/SRO, a single film of IrO₂, or a stackedfilm of IrO₂/SRO. If the upper electrode 23 is a stacked film ofIr/IrO₂, the materials may be deposited so that the layers have athickness of, for example, 10 and 20 nm.

Then, the hard mask layer 24 is deposited on the upper electrode 23 to athickness of about 500 nm. A desirable material for the hard mask layer24 is, for example, a PECVD-SiO₂ film, Al₂O₃ film, TiAlN film, aPECVD-SiO₂/Al₂O₃ film, a PECVD-SiO₂/TiAlN film.

Then, as shown in FIG. 5, a resist (not shown) is formed on the hardmask layer 24 and then patterned. The patterned resist is then used as amask to remove the hard mask layer 24 by anisotropic etching such as RIE(Reactive Ion Etching). Then, the patterned hard mask layer 24 is usedto remove the upper electrode 23, the ferroelectric film 22, the lowerelectrode 21, and the barrier film 20 by anisotropic etching such asRIE. In this case, the upper electrode 23, the ferroelectric film 22,the lower electrode 21, and the barrier film 20 are desirably etched ata time by changing etching conditions for the respective materials ofthe films. In this manner, the ferroelectric capacitor 25 a is formed inthe memory cell portion. The dummy ferroelectric capacitor 25 b isformed in the peripheral circuit portion. Then, a normal ashing processis used to remove the resist. Subsequently, annealing is executed at600° C. for one hour in order to eliminate possible damage done to thecapacitor 25 a during the capacitor processing.

Then, as shown in FIG. 6, the sputtering process is used to deposit theinsulating hydrogen barrier film 26 composed of, for example, Al₂O₃, toa thickness of about 20 nm. Then, the second interlayer insulating film27 composed of, for example, PECVD-SiO₂ film is deposited on thehydrogen barrier film 26 to a thickness of about 1,200 nm. Subsequently,the top surface of the second interlayer insulating film 27 is flattenedby CMP. At this time, the flattening may be carried out so that about500 nm of the second interlayer insulating film 27 is left on thecapacitors 25 a and 25 b.

Then, as shown in FIG. 2, the second interlayer insulating film 27, thehydrogen barrier film 26, and the hard mask layer 24 are partly etchedto form contact holes 28 a and 28 b through which the upper electrode 23is exposed. Then, annealing is executed at 600° C. for one hour in orderto eliminate possible damage to the capacitor 25 a owing to theformation of the contact holes 28 a and 28 b. This allows the diffusion,through the contact holes 28 a and 28 b, of unwanted volatile components(mainly H₂O, O₂ and the like) attributed to the interlayer insulatingfilm 18, deposited immediately below the hydrogen barrier film 26. Then,the first and second interlayer insulating films 18 and 27, the hydrogenbarrier film 26, and the gate insulating film 12 are removed byanisotropic etching to form a contact hole 29 through which thesource/drain diffusion layer 15 is exposed. Then, a barrier metal film(not shown) composed of Ti/TiN is formed in the contact holes 28 a, 28b, and 29. The MOCVD process is used to fill a metal material composedof tungsten, into the contact holes 28 a, 28 b, and 29. Then, the CMP isexecuted to flatten the metal material until the top surface of thesecond interlayer insulating film 27 is exposed. Thus, the contacts 30a, 30 b, and 30 d are formed. Then, a conventional technique such as asputter/anisotropic etching process or a damascene process is used toform the interconnects 31 a, 31 b, 31 c, 31 d, 31 e, and 31 f.Subsequently, required numbers of interlayer insulating films, contacts,and interconnects are provided to form a ferroelectric memory.

According to the above first embodiment, not only the capacitor 25 a andthe capacitor contact 30 a are formed in the memory cell portion, whichactually requires a capacitor, but the dummy capacitor 25 b and dummycapacitor contact 30 b, which do not perform circuit operations, areformed in a marginal area in the peripheral circuit portion, which doesnot actually require any capacitors. This produces the followingeffects.

(1) During the annealing step after the contact holes 28 a and 28 b havebeen formed, volatile components accumulated immediately below thehydrogen barrier film 26 can be diffused to the exterior of a waferthrough the contact hole 28 a, penetrating the hydrogen barrier film 26in the memory cell portion. By thus increasing the number of pathsthrough which volatile components are diffused, it is possible tocontrol released gases. Accordingly, even if the contact hole 29,penetrating the hydrogen barrier film 26, is formed after annealing, itis possible to suppress the explosive evaporation of volatile componentsthrough the contact hole 29. Thus, when the contact hole 29 is filledwith the metal material, it is possible to hinder voids from beingcreated by gasses resulting from volatile components. Therefore,inappropriate contacts can be avoided.

(2) In the prior art, during the step of flattening the interlayerinsulating film 27 after the capacitor has been formed, a step may beformed between a region with the capacitor and a region without thecapacitor. The step may result in inappropriate exposure in alithography step and thus improper contacts. In contrast, in the firstembodiment, the dummy capacitor 25 b is placed in the peripheral circuitportion, which inherently does not contain any capacitors. This servesto prevent the formation of a step between the memory cell portion andthe peripheral circuit portion during the step of flattening theinterlayer insulating film 27. It is thus possible to solve the problemsincluding inappropriate exposure and contacts.

The dummy capacitor 25 b is not limited to the peripheral circuitportion. It can be placed in any region which conventionally does notcontain any capacitors but which has a sufficient space.

Further, as shown in FIG. 7, if there is sufficient space, a pluralityof the dummy capacitors 25 b, 25 b and a plurality of the dummycapacitor contacts 30 b and 30 c may be provided.

Furthermore, as shown in FIG. 8, a contact 40 may be formed immediatelybelow the dummy capacitor 25 b simultaneously with the formation of thecontact 19 in the memory cell portion. In this case, it is also possibleto hinder the formation of a step between the memory cell portion andthe peripheral circuit portion when the interlayer insulating film 18 isflattened. Since the capacitor 25 b and the contacts 30 b and 40 must bein the floating state, the insulating film of the element isolationregion 13 is desirably formed under the contact 40.

Second Embodiment

A second embodiment is an example in which the evaporation of gasesaccumulated under the hydrogen barrier film is controlled by forming adummy capacitor in a peripheral circuit portion that conventionally doesnot contain capacitors or the like.

FIGS. 9 and 10 show a semiconductor memory device according to a secondembodiment of the present invention. As shown in FIGS. 9 and 10, thesecond embodiment is the same as the first embodiment except that in theperipheral circuit portion, no dummy capacitors but only dummy capacitorcontacts 30 b and 30 c are formed.

At least one end of each of the contacts 30 b and 30 c is notelectrically connected to other interconnects or elements and is in thefloating state. Consequently, no current flows through the contact 30 b.Further, the contacts 30 b and 30 c are provided through the hydrogenbarrier film 26 and do not reach the silicon substrate 11.

FIGS. 11 and 12 are sectional views of steps of manufacturing asemiconductor memory device according to a second embodiment of thepresent invention. Description will be given below of a method ofmanufacturing a semiconductor memory device according to the secondembodiment.

First, as shown in FIGS. 3 and 4, the barrier film 20, the lowerelectrode 21, the ferroelectric film 22, the upper electrode 23, and thehard mask layer 24 are sequentially deposited as in the case of thefirst embodiment.

Then, as shown in FIG. 11, a resist (not shown) is formed on the hardmask layer 24 and then patterned. The patterned resist is then used as amask to remove the hard mask layer 24 by anisotropic etching. At thistime, the hard mask layer 24 is left only in a region of the memory cellportion in which the capacitor is to be formed. Then, the patterned hardmask layer 24 is used to remove the upper electrode 23, theferroelectric film 22, the lower electrode 21, and the barrier film 20by anisotropic etching. In this case, the upper electrode 23, theferroelectric film 22, the lower electrode 21, and the barrier film 20are desirably etched at a time by changing etching conditions for therespective materials of the films. In this manner, the ferroelectriccapacitor 25 a is formed only in the memory cell portion. No dummycapacitors are formed in the peripheral circuit portion. Then, a normalashing process is used to remove the resist. Subsequently, annealing isexecuted at 600° C. for one hour in order to eliminate possible damagedone to the capacitor 25 a during the capacitor processing.

Then, as shown in FIG. 12, the sputtering process is used to deposit theinsulating hydrogen barrier film 26 composed of, for example, Al₂O₃, toa thickness of about 20 nm. Then, the second interlayer insulating film27 composed of, for example, PECVD-SiO₂ film is deposited on thehydrogen barrier film 26 to a thickness of about 1,200 nm. Subsequently,the top surface of the second interlayer insulating film 27 is flattenedby CMP. At this time, the flattening may be carried out so that about500 nm of the second interlayer insulating film 27 is left on thecapacitor 25 a.

Then, as shown in FIG. 10, the second interlayer insulating film 27, thehydrogen barrier film 26, and the hard mask layer 24 are partly etchedto form the contact hole 28 a through which the upper electrode 23 isexposed, and dummy contact holes 28 b and 28 c. In this case, for thedummy contact holes 28 b and 28 c, etching is controlled so that theirbottom portions lie inside the interlayer insulating film 18. Then,annealing is executed at 600° C. for one hour in order to eliminatepossible damage to the capacitor 25 a owing to the formation of thecontact holes 28 a, 28 b, and 28 c. This allows the diffusion, throughthe contact holes 28 a, 28 b, and 28 c, of unwanted volatile components(mainly H₂O, O₂, and the like) attributed to the interlayer insulatingfilm 18, deposited immediately below the hydrogen barrier film 26. Then,the first and second interlayer insulating films 18 and 27, the hydrogenbarrier film 26, and the gate insulating film 12 are removed byanisotropic etching to form the contact hole 29 through which thesource/drain diffusion layer 15 is exposed. Then, a barrier metal film(not shown) composed of Ti/TiN is formed in the contact holes 28 a, 28b, 28 c, and 29. The MOCVD process is used to fill a metal materialcomposed of tungsten, into the contact holes 28 a, 28 b, 28 c, and 29.Then, the CMP is executed to flatten the metal material until the topsurface of the second interlayer insulating film 27 is exposed. Thus,the contacts 30 a, 30 b, 30 c, and 30 d are formed. Then, theconventional technique such as the sputter/anisotropic etching processor the damascene process is used to form the interconnects 31 a, 31 b,31 c, 31 d, 31 e, and 31 f. Subsequently, required numbers of interlayerinsulating films, contacts, and interconnects are provided to form aferroelectric memory.

According to the above second embodiment, not only the capacitor contact30 a is formed in the memory cell portion, which actually requires acapacitor, but the dummy capacitor contacts 30 b and 30 c, which do notperform circuit operations, are formed in a marginal area in theperipheral circuit portion, which does not actually requires anycapacitors. Thus, during the annealing step after the contact holes 28a, 28 b, and 28 c have been formed, volatile components accumulated inthe interlayer insulating film 18 can be diffused to the exterior of awafer through the contact hole 28 a, penetrating the hydrogen barrierfilm 26 in the memory cell portion. By thus increasing the number ofpaths through which volatile components are diffused, it is possible tocontrol released gases. Accordingly, even if the contact hole 29,penetrating the hydrogen barrier film 26, is formed after annealing, itis possible to suppress the explosive evaporation of volatile componentsthrough the contact hole 29. Thus, when the contact hole 29 is filledwith the metal material, it is possible to hinder voids from beingcreated by gasses resulting from volatile components. Therefore,inappropriate contacts can be avoided.

The depths of the dummy contacts 30 b and 30 c can be varied asdescribed below provided that the dummy contacts penetrate the hydrogenbarrier film 26.

For example, as shown in FIG. 13, the dummy contacts 30 b and 30 c mayreach the silicon substrate 11 via parts of the element isolation region13 which are formed in the silicon substrate 11. In this case, theelement isolation region 13 can be used as a stopper for the formationof the contact holes 28 b and 28 c.

Further, as shown in FIG. 14, the contacts 30 b and 30 c may be formedso as to reach the gate insulating film 12. In this case, the gateinsulating film 12 in the memory cell portion may also be formed on thesilicon substrate in the peripheral circuit portion. Then, the gateinsulating film 12 may be used as a stopper for the formation of thecontact holes 28 b and 28 c.

Further, as shown in FIG. 15, the contacts 30 b and 30 c may be formedso as to reach the top surface of a film 18 a constituting a part of amultilayer film under the capacitor 25 a. In this case, a multilayercomposed of, for example, an SiN film 18 a and an SiO₂ film 18 b may beformed under the capacitor 25 a. Then, the SiN film 18 a may be used asa stopper for the formation of the contact holes 28 n and 28 c.

Furthermore, the hydrogen barrier film 26 may be formed above thecapacitor 25 a and 25 b. For example, the hydrogen barrier film 26 maybe directly formed on the capacitor 25 a and 25 b, and a layer may beformed between the hydrogen barrier film 26 and the capacitor 25 a and25 b.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1: A semiconductor memory device comprising: a semiconductor substratehaving a first region and a second region; a transistor placed in thefirst region of the semiconductor substrate; a first insulating filmformed on the semiconductor substrate in the first and second regionsand on the transistor; a first ferroelectric capacitor formed on thefirst insulating film in the first region and electrically connected tothe transistor; a hydrogen barrier film formed above the firstferroelectric capacitor and formed above the first insulating film inthe first and second regions; a contact penetrating the hydrogen barrierfilm in the first region and electrically connected to the firstferroelectric capacitor; a dummy contact which penetrates completelythrough the hydrogen barrier film in the second region and which is in afloating state; and a gate insulating film of the transistor formed onthe semiconductor substrate in the first and second regions, wherein thedummy contact reaches the gate insulating film. 2-20. (canceled)